This invention relates generally to plate type exchanger arrangements for containing a reaction zone and indirectly heating the reaction zone with a heat exchange fluid.
In many industries, like the petrochemical and chemical industries, contact of reaction fluids with a catalyst in a reactor under suitable temperature and pressure conditions effects a reaction between the components of one or more reactants in the fluids. Most of these reactions generate or absorb heat to various extents and are, therefore, exothermic or endothermic. The heating or chilling effects associated with exothermic or endothermic reactions can positively or negatively affect the operation of the reaction zone. The negative effects can include among other things: poor product production, deactivation of the catalyst, production of unwanted by-products and, in extreme cases, damage to the reaction vessel and associated piping. More typically, the undesired effects associated with temperature changes will reduce the selectivity or yield of products from the reaction zone.
Exothermic reaction processes encompass a wide variety of feedstocks and products. Moderately exothermic processes include methanol synthesis, ammonia synthesis, and the conversion of methanol to olefins. Phthalic anhydride manufacture by naphthalene or orthoxylene oxidation, acrylonitrile production from propane or propylene, acrylic acid synthesis from acrolein, conversion of n-butane to maleic anhydride, the production of acetic acid by methanol carbonylation, and methanol conversion to formaldehydexe2x80x94represents another class of generally highly exothermic reactions. Oxidation reactions in particular are usually highly exothermic. The exothermic nature of these reactions has led to many systems for these reactions incorporating cooling equipment into their design. Those skilled in the art routinely overcome the exothermic heat production with quench or heat exchange arrangements. Extensive teachings detail methods of indirectly exchanging heat between the reaction zone and a cooling medium. Indirect heat exchange refers to the transfer of heat from one fluid to another fluid across a common surface without intermixing of the fluids as normally occurs in quench systems. The art currently relies heavily on tube arrangements to contain the reactions and supply indirect contact with the cooling medium. The geometry of tubular reactors poses layout constraints that require large reactors and vast tube surfaces to achieve high heat transfer efficiencies.
Other process applications accomplish indirect heat exchange with thin plates that define channels. The channels alternately retain catalyst and reactants in one set of channels and a heat transfer fluid in adjacent channels for indirectly heating or cooling the reactants and catalysts. Heat exchange plates in these indirect heat exchange reactors can be flat or curved and may have surface variations such as corrugations to increase heat transfer between the heat transfer fluids and the reactants and catalysts. Many hydrocarbon conversion processes will operate more advantageously by maintaining a temperature profile that differs from that created by the heat of reaction. In many reactions, the most beneficial temperature profile will be obtained by maintaining substantially isothermal conditions. In some cases, a temperature profile directionally opposite to the temperature changes associated with the heat of reaction will provide the most beneficial conditions. For such reasons, it is generally known to contact reactants with a heat exchange medium in cross flow, co-current flow, or counter current flow arrangements. A specific arrangement for heat transfer and reactant channels that offers more complete temperature control can be found in U.S. Pat. No. 5,525,311, the contents of which are hereby incorporated by reference. Other useful plate arrangements for indirect heat transfer are disclosed in U.S. Pat. Nos. 5,130,106 and 5,405,586.
Isolating reactants from coolants at the inlets and outlets of plate exchanger arrangements leads to elaborate designs and intricate manufacturing procedures. Simplification of the fluid transfer at the inlets and outlets of plate exchanger improves the cost effectiveness and practicality of plate exchanger usage in many processes. Improved arrangements for injecting reactants at intermediate locations along the process flow path can also improve reactor performance in terms of selectivity and yields.
It is, therefore, an object of this invention to simplify a plate exchanger design for the indirect heat transfer and injection of reactants in reaction zone.
It is a further object of this invention to simplify the feed and recovery of reactants and heat exchange fluid from a heat exchange reactor that uses a channel arrangement.
In broadest terms, this invention incorporates intermediate injection of process fluids into open chamber portions that circulate fluid from a plurality of heat exchange channels to another plurality of heat exchange channels to control process reaction conditions and reactant concentrations. A chamber communicates the heated channels and the reaction zone across common ends of the narrow channels while simultaneously mixing reactants the ends of the channels to provide simple transfer of fluids between different sets of channels. The chamber permits additional temperature control by the addition or removal of reactants, cooling fluids or other streams at an intermediate point in the complete channel flow paths. Insertion of additional chambers along the flow path of either the reaction or heated channels provides locations for more temperature adjustment and control.
Suitable channel arrangements may exchange heat directly across a common heat exchange surface or may use an intermediate heat transfer fluid to indirectly transfer heat from a cooling or heating zone to the reaction zone. In this manner the intermediate heat transfer fluid allows optimization of conditions for endothermic and exothermic reactions in different channels while simultaneously providing temperature adjustment control for differences in heat generation from the exothermic reaction and heat absorption from the endothermic reaction. For example, one arrangement of the intermediate heat transfer fluid may place the cooling zone and the reaction zone at different portions of common channel and may pass the intermediate fluid through adjacent channels to transfer heat out of reaction channels at one location and transfer heat back into the heated channels at a downstream channel location. In other arrangements, the intermediate channels and the reaction channels may lie in a parallel arrangement between the heated channels to adjust the temperature in the reaction channels through the heated channels.
Variation of the catalyst loading within the reaction channels and the addition of catalyst for endothermic reactions may satisfy different processing objectives. For example, short loading of catalyst in reaction channels can provide a space above or below the reaction zone for additional feed preheat or effluent cooling. Again, extending the heated channels can provide additional surface area for open channel heat exchange against the exiting reaction zone effluent or the incoming reactants.
Although usefull in any heat producing reaction or heat absorbing reaction, this invention finds its greatest benefit in exothermic reactions. As an example, process and reactor arrangements in accordance with this invention may be especially usefull for producing ethylene oxide. A particularly beneficial process application for this invention is in the production of phthalic anhydride (PA) by the oxidation of orthoxylene. The reaction apparatus feeds the orthoxylene feed to a distribution manifold that injects a controlled amount of orthoxylene in admixture with the air or other oxygen containing gas. Injection of the orthoxylene into the manifold prevents the presence of the orthoxylene and oxygen in explosive proportions. The manifold preferably contains a packing making, such as inert particles, to reduce the volume of the chamber and minimize the amount of mixed orthoxylene and oxygen. The plate arrangement of the heat exchange reactor quickly dissipates the high heat of reaction associated with the synthesis of the PA. The enhanced temperature control improves product selectivity while also permitting increased throughput.
The reaction apparatus designed in accordance with this invention offers a high degree of flexibility in temperature control with a relatively simple plate reactor arrangement. The outer containment vessel can completely support the plate arrangement from either its top or bottoms Direct passage of heated reactants from the heated channels outlets to reaction channels inlets through a common chamber eliminates the need for manifolding and its associated welding at at least one end of the typically thin channel plates.
The presence of narrow heat exchange channels for cooling the reaction zone and heating the reactants constitutes an essential requirement of this invention. With respect to fluid flow through the reaction channels and heated channels, fluid may have co-current flow or cross flow with respect to some of the channels. The plates defining the channels for containing the reactions and heat exchange gases may have any configuration that produces narrow channels. A preferred form of the beat exchange elements is relatively flat plates having corrugations defied therein. The corrugations serve to maintain spacing between the plates while also supporting the plates to provide a well supported system of narrow channels. Additional details on the arrangement of such plates systems are shown in U.S. Pat. No. 5,525,311, the contents of which are hereby incorporated by reference.
One distinct advantage discovered with the plate heat exchanger design of this invention permits an increase in the overall feed rate of oxidated reactants without increasing their overall concentration in feed stream mixtures that comprise air or oxygen. Notably for production of PA, the process and plate reactor arrangement of this invention significantly increases the amount of orthoxylene that can enter the reaction zone for a given constant air feed rate to the reaction channels.
Suitable plate arrangements may also incorporate perforated plates. Most advantageously, perforated plates allow the controlled quantities of the heated reactant to flow directly into the reaction channels. Perforated plates disperse the introduction of the reactant over a desired portion of the reaction zone. Those skilled in the art will recognize other variations in plate configurations that can provide additional benefits to the integrated reaction stages.
Accordingly, in a broad process embodiment, this invention contacts reactants with a catalyst in a reaction zone while indirectly heating or cooling the reactants in the reaction zone by indirect heat exchange with a heat exchange fluid. The process passes a reactant-containing stream through a first plurality of channels defined by spaced apart plates and recovers a first channel effluent. A first channel effluent stream collects in a manifold volume having direct communication with outlets of the first plurality of channels. The process injects an intermediate fluid into the manifold volume and mixes at least a portion of the first channel effluent to produce a second channel input stream. The second channel input stream passes from the manifold volume directly into the inlets of a second plurality of channels defined by spaced apart plates. The process recovers a second channel effluent stream from the outlets of the second portion of spaced apart plates. At least the reactant stream or the second channel input stream contacts a catalyst in the first plurality of channels or the second plurality of channels. The process indirectly exchanges heat between the reactant-containing stream, the second channel input stream, and a heat exchange fluid passing through channels defined by the spaced apart plates.
In a more specific process embodiment, this invention is a process for oxidizing reactants with a catalyst in a reaction zone while indirectly cooling the reactants in the reaction zone by indirect heat exchange with a heat exchange fluid. A first inlet stream containing oxygen and an oxidation reactant passes through a first plurality of channels defined by spaced apart plates and into contact with an oxidation promoting catalyst. An effluent from the outlets of the first plurality of channels passes directly into a manifold volume containing a packing material. The process injects additional oxidation reactant into the manifold volume and mixes fluids therein to produce a second inlet stream containing oxygen and an oxidation reactant. The second inlet stream passes from the manifold volume directly to the inlets of a second plurality of channels defined by the spaced apart plates and through an oxidation promoting catalyst contained in the second plurality of channels. The process recovers a second channel effluent stream from the outlets of the second portion of spaced apart plates and indirectly exchanges heat with the first and second plurality of channels by passing a heat exchange fluid through the heat exchange channels defined by the spaced apart plates. In a preferred form of the exothermic process, the first inlet stream comprises air and orthoxylene; the intermediate stream comprises orthoxylene; and the first and second plurality of channels contain an orthoxylene oxidation catalyst that promotes the production of the second channel effluent comprising phthalic anhydride.
A specific apparatus embodiment of this invention is a particular plate reactor design that advantageously uses the chamber design of this invention to independently pass at least two different fluids through two adjacent sets of channels in counter-current flow. The specific reactor arrangement may use a perforated manifold arrangement to enhance the even distribution of entering reactants.
In a more complete apparatus embodiment, this invention is a reaction arrangement for contacting reactants with a catalyst in a reaction zone while indirectly heating or cooling the reactants in the reaction zone by indirect heat exchange with a heat exchange fluid. The apparatus comprises a plurality of spaced apart plates that define a first plurality of reaction channels and a second plurality of reaction channels for retaining a catalyst material in at least one of the first and second plurality of channels. The first plurality of reaction channels defines a first plurality of reaction inlets and a first plurality of reaction outlets. The second plurality of reaction channels defines a second plurality of reaction inlets and a second plurality of reaction outlets. The apparatus includes a distribution manifold defining a manifold volume in direct communication with the fist plurality of reaction outlets and with the second plurality of reaction inlets and containing an injector for injecting a fluid into the manifold volume. In a more limited form of this apparatus embodiment the plurality of plates defines heat exchange channels between the first and second plurality of reaction channels and the heat exchange channels define heat exchange inlets for receiving a heat exchange fluid and heat exchange outlets for discharging a heat exchange fluid. A particularly beneficial arrangement of manifolds uses a first distribution header that partially covers one side of a stack of heat exchange plates defined by the plurality of plates. The first distribution header extends across at least one of the heat exchange inlets or heat exchange outlets to define a first distribution space that communicates directly with the inlet or outlet across which it extends to distribute or collect the heat exchange fluid. A second distribution header partially covers the one side of the stack of heat exchange plates and partially covers at least a portion of the first distribution header. The second distribution header extends across at least one of the first reaction inlets or the first reaction outlets to define a second distribution space that communicates directly with the inlet or outlet across which it extends to distribute or collect fluid.
Additional embodiments, arrangements, and details of this invention are disclosed in the following detailed description of the invention.